Regulation of calcium homeostasis and the unfolded protein response (UPR) are two processes of particular importance in neuronal pathophysiology. Stanniocalcin 2 (STC2) is a secreted glycoprotein thought to play a role in calcium homeostasis. Expressed as part of the UPR, STC2 is also induced in the rat brain after middle cerebral artery occlusion and knockdown of STC2 expression sensitizes cells to hypoxia and endoplasmic reticulum stress. Since STC2 is involved in both the UPR and calcium regulation, this protein may play a particularly important role in the nervous system. The objective of this proposal is to elucidate the function of STC2, with special emphasis on its possible role in neuronal pathophysiology. Aim 1: Investigate the effect of STC2 expression on STIM1 function My preliminary data demonstrates that loss of STC2 expression leads to an increase in calcium entry through store-operated calcium channels (SOCs) and that STC2 can interact with the ER calcium sensor STIM1. Therefore, I will test the hypothesis that STC2 affects calcium entry by altering STIM1 mediated regulation of SOCs. Specifically, I will conduct live cell imaging experiments to measure translocation of STIM1 after store depletion in the presence or absence of STC2 expression. I will also test the effect of STC2 expression on the interaction between ST1M1 and SOCs by measuring FRET between STIM1 and SOCs before and after calcium store depletion. Aim 2: Characterize STC2 mediated effects on calcium homeostasis following glutamate exposure STC2 is expressed in the brain following injury and plays a cytoprotective role in cultured cells. In addition, loss of STC2 expression leads to a significant increase in calcium influx. Therefore, I will test the hypothesis that STC2 mediated regulation of calcium homeostasis is important for neuronal survival in the context of calcium dependent neuronal injury. I will compare changes in [Ca2+]i levels between STC2+/+ and STC2-/- neurons following exposure to glutamate. I will also use inhibitors of store-operated calcium entry to determine the importance of this pathway in STC2 mediated effects on glutamate-induced neuronal injury.